Nuclear reactor moderator structures



Dec. 24, 1963 s. HACKNEY ETAL NUCLEAR RRAcToR MoDRRAToR STRUCTURES Filed July 1, 1958 JllllllJ I.

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......T.M.Iii k 2 s Uw w y @MMWR mow/m Mm A mm mm BY Qfrc/ lli Patented Dec. 2dr, i963 NUC'LEAR REACTR MDEFLATR STRUCEURES Stanley Haclmey, Fearnhead, Warrington, and Peter P eil Munn, Culeheth, near Warrington, England, assignors to the United Kingdom Atomic Energy Authority, Lon-s don, England Filed `idly l, M52-, Ser. No. '745,853 Claims priority, application Great Britain .luly l, H57 3 Claims. (Cl. 26d-193.2)

This invention relates to nuclear reactors and it provides a radially-acting restraint device for a graphite moderator structure.

A conventional moderator and reilector structure comprises stacks of uniform right prismatic bloei-is positioned in layers extending in the direction of the length of the blocks, the blocks in the moderator part being suitably spaced to allow for growth under the effects of irradiation. Such a structure is not in itself stable and the instability is aggravated by the passage of a gas coolant through the structure which tends `to blow it apart and by growth of the graphite under irradiation etects. Accordingly a radially-acting restraint has to be provided to keep the structure stable whilst allowing for dimensional changes in the lifetime of the reactor.

Current nuclear reactor design uses a restraint in the form of a series of garters and elastic bands, the design being made as simple and robust as possible on the basis that maintenance and adjustment is not practicable. Such designs inevitably require elastic members to be provided in a region of substantial neutron and gamma llux and the lbehaviour of elastic members in these conditions is not fully understood at this time. Similarly, the behaviour of the graphite structure itself under condition oi prolonged irradiation is not fully established and tnere are even reasons to believe that shrinkage of the graphite may eventually occur.

According to the present invention a radially-acting restraint device for a graphite moderator structure comprises a series of wedges arranged to impose radially-act ing restraint forces between a graphite moderator st-ruc- `ure and a containing vessel, and means for applying forces -to the wedges comprising a thrust rod contained within a tube and loaded by a spring in the tube, the tube and rod being of a length to allow the spring to operate in a zone protected by shielding from radiations yfrom the reactor and accessible from outside said shielding.

rl`he invention will now be described with reference to the accompanying drawings wherein FIG. l is a sectional View and FlG. 2 is a perspective view in which the plane of the section of FlG. l is indicated by the line I.

`ln FIG. l a series of Wedges itl is arranged to impose radially-acting restraint forces between a graphite moderator structure ll and its containing vessel l2. Forces are applied to the wedges d@ by a thrust rod 13' contained within a guide tube 14 and loaded by a spring l5. The rod i3 and tube ld pass through a reactor pressure vessel 29 and radiation shielding Sil.

The thrust rod i3 has a rounded end i6 and bears on a 'bearing cap l? mounted on a .thrust plate i3. The thrust plate l carries scre -threaded adjusting pins 19 with square ends 24 and rounded ends 2li. The rounded ends 2li bear on bearing caps 2l mounted on plates 22 on the wedges lll and are held in the caps 2d by pins 23.

Locknuts 25 are provided above ythe thrust plate 1S. The wedges il? (shown also in FIG. 2) comprise, in eect, cuboids divided into three parts by two cuts each starting along the same diagonal of the top face of the cuboid and finishing respectively near the corners lying at the ends of a transverse diagonal of the bottom face of the cuboid, the knife edges of the three parts being removed. This arrangement provides a wedge shaped piece 26 acting against two identical members 27, the top two members 2,7 having extensions 2d on which the plates 2.2 are txed. Each wedge shaped piece 26 rests on the two members Z7 below it so that the load is transmitted through pieces 2.6 and members 27 alternately and as the load on the pieces 26 becomes heavier the angle of the cuts dividing the cuboid is made more acute. A ring of wedge assemblies is provided around each layer or graphite blocks.

The thrust rod 13 and guide rod 'i011 pass through the reactor pressure vessel 29 and radiation shielding 36. A strengthening sleeve d1 is kwelded to the guide rod 14 and to the pressure vessel Z9. The spring d5 loading the rod i3 is housed in a spring housing 3d located in the shielding 3d so as to be well shielded from. the reactor. The housing 3l is welded to the guide tube i4.

The spring operates through a flanged plug 32 screwed and welded on an extension 33 on the rod i3 and is adjusted by means of a spring compression plug 34 screwed into the housing 3l. and sealed by a sealing ring 35. A hole 36 is provided for rotating the plug 3d with a key fitting in lthe hole. A cap 37 with a sealing ring 38 is clamped over the housing 3d -by a ring 39 with castellations 4i).

ln the assembly of the restraint device the screws 19 are adjusted to bring the thrust plate 1S level and the screws are then secured with pins 23 `and lock-nuts 25. The rod i3 and its spring assembly is made up and the compression plug 3 adjusted to give a predetermined detlection to the spring l5. The .cap 37 is then clamped in position with the ring 3% to seal the tube d4. Thus restraint is exercised on the moderator structure ll through the springs i5, plug 32 rod i3, bearing cap i7, thrust plate ld, pins i9, caps 2l, plates 22 and wedges lll. in the wedges le the members Z7 take up positions relative to the wedge shaped pieces 26 depending on the load applied by compression or" the spring l5 and as growth takes place in the moderator structure so slip occurs on the faces of the Iwedges to increase the compression of the spring l5. From time to time the compression may be decreased by unsc-rewing the cap 3d in addition to the restraint applied whilst accommodating Wigner growth the restraint device described above also accommodates the thermal growths occurring during warming up of the reactor when the containing vessel d2 expands more than the graphite moderator structure which would normally cause substantial reduction of the initial restraining forces, or, in the absence of strong initial restraint forces, the removal of restraint altogether.

We claim:

l. in a nuclear reactor having a moderator structure within a containing vessel, means for restraining movenient of the moderator structure in the direction radial or" the containing vessel, said restraining means comprising a series of wedges disposed in the moderator structure and displaceable in a direction normal to said radial direction to accommodate moderator structure expansion in said radial direction, and means for engaging said wedges to control the extent of displacement thereof in said direction normal to said radial direction and thus accommodate radial xpansion of said moderator structure, said means engaging said wedges including wedge bearing means applying torce on the wedges in a direction nor-mal to said radial direction, means for loading said wedge lbearing means, and means tor adjusting said loading means.

2. A nuclear reactor according to claim yl wherein the series of wedges includes a cuboid divided into three parts by two cuts each starting along the same diagonal of [the top face of the cuboid and finishing respectively near the corners lying at the ends of a transverse diagonal of the References Cited in the le of this patent UNITED STATES PATENTS Wundrack May 2,1, V1918 4 Dobie Aug. 18, 1924 Frisch et al. Feb. 7, 1933 Long et al. June 10, 1958 Long et al. Sept. 16, 1958 Hughes Sept. 23,1958 `Correo Jan. 31, 1961 FOREIGN PATENTS Great Britain Nov. 6, 1957 

1. IN A NUCLEAR REACTOR HAVING A MODERATOR STRUCTURE WITHIN A CONTAINING VESSEL, MEANS FOR RESTRAINING MOVEMENT OF THE MODERATOR STRUCTURE IN THE DIRECTION RADIAL OF THE CONTAINING VESSEL, SAID RESTRAINING MEANS COMPRISING A SERIES OF WEDGES DISPOSED IN THE MODERATOR STRUCTURE AND DISPLACEABLE IN A DIRECTION NORMAL TO SAID RADIAL DIRECTION TO ACCOMMODATE MODERATOR STRUCTURE EXPANSION IN SAID RADIAL DIRECTION, AND MEANS FOR ENGAGING SAID WEDGES TO CONTROL THE EXTENT OF DISPLACEMENT THEREOF IN SAID DIRECTION NORMAL TO SAID RADIAL DIRECTION AND THUS ACCOMMODATE RADIAL EXPANSION OF SAID MODERATOR STRUCTURE, SAID MEANS ENGAGING SAID WEDGES INCLUDING WEDGE BEARING MEANS APPLYING FORCE ON THE WEDGES IN A DIRECTION NORMAL TO SAID RADIAL DIRECTION, MEANS FOR LOADING SAID WEDGE BEARING MEANS, AND MEANS FOR ADJUSTING SAID LOADING MEANS. 